Linear actuators create motion in a straight line, in contrast to the circular motion of a conventional electric motor. Such actuators are designed for use where a motor drives a threaded shaft and a corresponding threaded coupled nut such that rotary motion of a control knob or handle is converted into a linear displacement via screws, gears or other similar devices. Most electro-mechanical linear actuator designs incorporate ball screws and ball nuts. The screw may be connected to a motor or manual control knob either directly or through a series of gears. Gears are typically used to allow a relatively small motor spinning at a higher rotational speed to be geared down to provide the torque necessary to spin the screw under a heavier load than the motor would otherwise be capable of driving directly.
Various methods have been attempted to interface a screw to a motor rotor that maintains axial load capacity and controls critical runout which in turn affects accuracy and repeatability of system. These prior art interface attempts include a press fit, a weld and an adhesive.
The press fit requires critical tolerance between shaft and hole which add cost and are hard to maintain in a motor shaft given the small diameter bore and long span. Press fits also applies high loads to motor bearings which may damage the bearings or affect system accuracy.
The weld requires a welded joint having similar metals and precision machined interface to ensure accuracy and runout. The welding method is labor intensive, requires specialized equipment and tooling, and must be assembled prior to motor assembly to protect motor from welding current.
The adhesive method involves adhesives that may be used to bond the screw to motor but also requires a precision interface, additional surface preparation, and cure time. The adhesive method also achieves the lowest strength and torque transmission capability.
Each of these prior art methods for attaching the screw to the motor is considered a permanent solution as once the interface is achieved, risk of system damage prevents disassembly and continued use of used components.
Unfortunately, linear actuators typically require a relatively complex interface between the screw and motor rotor, making assembly and disassembly of the system a time consuming process. In addition, typical linear actuators do not provide high levels of precision during operation.
This disclosure describes improvements over these prior art technologies.